It is well known that 80% to 90% of North American buses utilize a 2-stroke diesel engine of the kind manufactured by Detroit Diesel. However, the level of permitted emissions in North America will become more and more stringent over the next few years, and there is serious concern that many of the 2-stroke diesel engines currently in use will not be able to meet the new standards. The primary difficulties with the standard 2-stroke diesel engines relate to emitted "smoke" (unburned carbon) and NO.sub.x.
A significant prior art patent is U.S. Pat. No. 4,527,516, issued July 9, 1985 to Foster. However, this prior patent does not address the optimization of engine operation with respect to low emissions, and does not provide any means for accomplishing such optimization. Furthermore, this prior patent fails to appreciate the importance of cooling the combustion air prior to injection.